1. Field of the Invention
The present invention relates to wafer carrier systems used in the semiconductor industry and more particularly, to suspended cantilever paddle systems.
2. Description of the Prior Art
In the manufacture of silicon and other types of wafers used in semiconductor industries, wafers are subjected to relative high temperatures for specific periods of time. Wafer fabrication furnaces are used to generate the necessary heat. The wafers are placed within the furnaces in boats or wafer carriers which are supported and suspended within the furnace by boat suspension systems or paddles.
At present, there are two types of paddles used in the semiconductor industry, a wheelbarrow design and a totally suspended cantilever design. The present invention relates more to the cantilever than the wheelbarrow paddle.
As new means are developed to increase the amount of electronic circuits on a silicon "chip" the purity of the silicon wafer, the base or platform of the "chip", becomes critical. If wafer impurities are not kept at acceptable tolerances, contaminated wafers must be rejected and destroyed resulting in high wafer fabrication costs. Only through strict purity control can wafer impurities be kept to a minimum and wafer yields optimized.
To reduce the impurities in wafer manufacture, particulate generation must be maintained at the lowest levels possible. The cantilever paddle design, unlike the wheelbarrow design, reduces particulate generation in the fabrication of silicon wafers. To reduce particulate generation, the cantilever paddle design eliminates all contact between the paddle, the boat or the wafers themselves with the interior walls of the diffusion tube. This elimination of contact between the wafer carrier system and the diffusion tube is accomplished by supporting the paddle at only one end of the system.
Conventional cantilever design utilizes two sleeved support members to suspend and support the paddle within the diffusion tube. The support members incorporate materials such as silicon carbide, aluminum oxide and quartz. The combined use of these materials is necessary to achieve the required structural rigidity in the support section of the paddle to minimize deflection of the paddle at its unsupported end. In some applications, the unsupported end of the paddle can extend over sixty inches in length.
Temperatures within the fabrication furnace have conventionally ranged from 600.degree. C. to 900.degree. C. More recently, due to advances in electrical circuit design, furnace temperatures have increased to between 900.degree. C. and 1300.degree. C.
While conventional paddle design is adequate for some wafer manufacture, it has serious drawbacks. One such disadvantage of a conventional cantilever paddle design relates to high particulate generation, especially in high temperature fabrication, due to outgasing by the conventional composite support members.
Another disadvantage of the conventional cantilever paddle design concerns the insufficient structural support provided by the conventional support and suspension members over the length of the paddle. The insufficient support results in paddle deflection at the unsupported end of the paddle causing improper positioning of the wafers within the furnace, thereby decreasing wafer yield, and in extreme cases, resulting in contact between the paddle and the furnace wall. As discussed above, such contact between the paddle and the furnace wall percipitates undesired and detrimental particulate generation that the cantilever paddle design is utilized to avoid.
A further disadvantage of the conventional cantilever paddle design concerns how difficult it is to clean. The difficulty is due to the design of the paddle which integrates the support and suspension members of the paddle into one unified structure. In this configuration, total disassembly of the paddle must be accomplished before the suspension members of the paddle can be disengaged from the system for cleaning resulting in lost production time.
Another disadvantage of the conventional cantilever design concerns its inability to easily accept different wafer boat configurations due to the integral design of its support and suspension members resulting in less efficient wafer manufacture.